Basic phenates are generally used in lubricating oils for internal combustion engines, and exhibit a marked effect in preventing corrosive wear, formation of piston ring groove deposits, piston ring sticking, etc., by neutralizing or dispersing acids such as oxyacids or sulfuric acid, sludge, lacquers, carbon, etc.
From the standpoint of the function of acid neutralization, phenates can be classified into two types, one type being called normal phenates containing a theoretical amount, one gram equivalent, of metal per equivalent of phenolic hydroxyl group; and the other type being called basic phenates or over-based phenates, e.g., as disclosed in U.S. Pat. No. 3,464,970 and British Pat. No. 1,280,749, containing metal in an amount larger than the theoretical amount, wherein a theoretical amount is considered the reaction of 1 gram equivalent of alkaline earth metal reacted per equivalent of phenolic hydroxyl group. The present invention relates to a novel process for preparing basic or over-based phenates containing metal in an amount larger than the theoretical amount.
Heretofore, two typical methods for introducing sulfur into phenates have been known. One method comprises converting an alkyl phenol to the sulfide thereof using sulfur chloride, for example, and, thereafter, converting the sulfide to a metal salt. The other method comprises sulfurizing the phenol at the time of adding a metal or sulfurizing the metal salt (phenate) using elemental sulfur. The present invention is based on the latter method of sulfurization.
A number of techniques have been developed to produce over-based phenates by the latter method of sulfurization. It is now possible to produce over-based phenates containing an alkaline earth metal in an amount of at least two times the theoretical amount based on the hydroxy group of phenols by the one-step reaction. U.S. Pat. Nos. 3,464,970 and 3,725,381, and Japanese Pat. Nos. 533079 and 613543, for example, disclose that over-based phenates which contain the metal added in an amount of at least two times the theoretical amount based on the phenol and which are stable and oil-soluble can be prepared by performing a sulfurization reaction and a metal addition reaction at the same time in the presence of a higher alcohol solvent and then treating the reaction product with carbon dioxide. In addition, U.S. Pat. No. 4,123,371 discloses that if the above-described reactions are conducted in the presence of excess amounts of phenols, there can be prepared alkaline earth metal phenates of unexpectedly high basicity.
In these methods, however, if it is desired to increase the conversion or incorporation of an alkaline earth metal agent into the product per reaction cycle (which is hereinafter referred to as a "product conversion"), it is required for the dihydric alcohol being used for the metal addition reaction to be added in a larger excess amount than that actually consumed for the preparation of the desired product. When the reaction product is treated with carbon dioxide after the metal addition reaction, if a large amount of dihydric alcohol exists in the reaction system, or if a large amount of dihydric alcohol remains in the ultimate product, the stability of the product is reduced. It is, therefore, necessary to distill away an excess of dihydric alcohol after the completion of the metal addition reaction. In general, however, the removal of the high boiling dihydric alcohol by distillation requires a long period of time. Thus, the utilities required for this purpose are increased, and moreover it leads to a serious reduction in the yield of the phenate per unit time. In addition, the use of an excess of dihydric alcohol for the metal addition reaction results in a decrease in the yield of the phenate per unit volume of the reactor.
Decreasing the amount of the dihydric alcohol to be used in the conventional methods for the purpose of avoiding the above-described problems yields another problem that the product conversion of the alkaline earth metal agent drops. This drop in the product conversion of the alkaline earth metal agent leads to the formation of insoluble materials in the course of the reaction. The alkaline earth metal agent converted into such insoluble materials cannot be recycled and reused unlike the phenols and dihydric alcohol. This leads to a decrease in the yield of the basic phenate. Moreover, if large amounts of insoluble materials are present, the operation of removing them becomes troublesome.
As a result of extensive investigations to overcome the above-described problems, it has been found that if water is added to the reaction system at the time of performing the metal addition reaction of an alkaline earth metal agent with phenols, the metal addition reaction proceeds smoothly even if the amount of the dihydric alcohol being used is decreased. Further, the product conversion of the alkaline earth metal agent can be maintained at a high level, and the time and utilities required for the distillation of the reaction product after the completion of the metal addition reaction can be greatly reduced. Accordingly, basic or over-based alkaline earth metal phenates or sulfurized alkaline earth metal phenates (hereinafter collectively referred to as "basic alkaline earth metal phenates") can be produced advantageously from an industrial standpoint.
It is known that in the sulfurization and metal addition reaction of phenols using phenols, dihydric alcohols, elemental sulfur, and an alkaline earth metal agent, as the reaction proceeds, water is formed in a nearly equimolar amount to that of the alkaline earth metal agent reacted. Heretofore, the water thus-formed has ordinarily been removed simultaneously with the formation thereof. Water is almost incapable of dissolving an alkaline earth metal agent such as a calcium agent and does not serve as a solvent. Conversely, water has been considered to be an obstacle lowering the dissolution ability of other solvents. Although the mechanism for the sulfurization and metal addition reaction and the chemical structure of the product are not fully understood at the current time, it could not have been expected at all from the water being formed during the reaction that the addition of a suitable amount of water prior to the start of the reaction or in the course of the reaction produces a marked effect of accelerating the progress or completion of the reaction. Thus, the present invention is based on the unexpected and new discovery as described above.